The present invention is directed toward methods and apparatuses for irradiating a microlithographic substrate, and in particular, methods and apparatuses for irradiating the microlithographic substrate while moving it axially relative to a radiation source. Microelectronic features are typically formed in microelectronic substrates (such as semiconductor wafers) by selectively removing material from the wafer and filling in the resulting openings with insulative, semiconductive, or conductive materials. One typical process includes depositing a layer of radiation-sensitive photoresist material on the wafer, then positioning a patterned mask or reticle over the photoresist layer, and then exposing the masked photoresist layer to a selected radiation. The wafer is then exposed to a developer, such as an aqueous base or a solvent. In one case, the photoresist layer is initially generally soluble in the developer, and the portions of the photoresist layer exposed to the radiation through patterned openings in the mask change from being generally soluble to become generally resistant to the developer (e.g., so as to have low solubility). Alternatively, the photoresist layer can be initially generally insoluble in the developer, and the portions of the photoresist layer exposed to the radiation through the openings in the mask become more soluble. In either case, the portions of the photoresist layer that are resistant to the developer remain on the wafer, and the rest of the photoresist layer is removed by the developer to expose the wafer material below.
The wafer is then subjected to etching or metal disposition processes. In an etching process, the etchant removes exposed material, but not material protected beneath the remaining portions of the photoresist layer. Accordingly, the etchant creates a pattern of openings (such as grooves, channels, or holes) in the wafer material or in materials deposited on the wafer. These openings can be filled with insulative, conductive, or semiconductive materials to build layers of microelectronic features on the wafer. The wafer is then singulated to form individual chips, which can be incorporated into a wide variety of electronic products, such as computers and other consumer or industrial electronic devices.
As the size of the microelectronic features formed in the wafer decreases (for example, to reduce the size of the chips placed in the electronic devices), the size of the features formed in the photoresist layer must also decrease. This requires focusing the radiation impinging on the photoresist layer more sharply. However, as the radiation is more sharply focused, it loses depth of focus. As a result, only the top stratum of the photoresist layer may be adequately exposed to the sharply-focused radiation, and the lower strata of the photoresist layer may not be adequately exposed. Accordingly, the edges of those portions of the photoresist layer that remain on the wafer after the wafer is exposed to the solvent can become indistinct. This in turn can adversely affect the definition of the microelectronic features formed on the wafer.
One approach to addressing the foregoing problem (a xe2x80x9cstepperxe2x80x9d approach) has been to expose one or more relatively large fields of the wafer to the incoming radiation, and then move the wafer axially relative to the incoming radiation so that the focal plane of the radiation passes through several strata of the photoresist layer. This process is generally referred to as xe2x80x9cfocus drilling.xe2x80x9d In one specific application of this principle (termed focus latitude enhancement exposure or xe2x80x9cFLEXxe2x80x9d), the wafer is placed on a stepper stage and one field of the wafer is exposed to light passing through a mask and focused at a given depth. The focal plane is then changed to be at a different depth, and the field is re-exposed. This process is repeated sequentially for a number of focal plane depths. Alternatively, the wafer can be moved axially as it is being exposed. In either case, the stepper then moves the wafer to expose another field of the wafer and the process is repeated until all the fields of the wafer are exposed. Further details of the FLEX process are disclosed in a publication titled xe2x80x9cImprovement of Defocus Tolerance in a Half-Micron Optical Lithography by the Focus Latitude Enhancement Exposure Method: Simulation and Experimentxe2x80x9d (Hiroshi Fukuda et al., July 1989). One drawback with the foregoing method is that it is performed on a stepper apparatus. Accordingly, the resolution of the features may be limited because an entire field of the wafer must be accurately imaged with each exposure.
Another approach to addressing the foregoing problem (a xe2x80x9cscannerxe2x80x9d approach) is to move the wafer along an inclined path as the wafer and the mask scan past each other to align successive portions of the mask with corresponding successive portions of the wafer passing below. U.S. Pat. No. 5,194,893 to Nishi discloses a scanner method for altering the axial position of the depth of focus relative to the photoresist layer as the wafer moves relative to the mask. According to this method, the wafer is canted relative to the incoming radiation so that the focal plane passes through more than one strata of the photoresist layer as the wafer and the mask move relative to each other. The scanner approach can be more accurate than the stepper approach because only a small portion of the mask must be imaged at any given time. However, a drawback with the foregoing approach is that it may not provide the desired level of control over the position of the focal plane.
The present invention is directed toward methods and apparatuses for exposing a radiation-sensitive material of a microlithographic substrate to a selected radiation. In one embodiment, the method can include directing the radiation along a reticle radiation path segment toward a reticle. The method can further include passing the radiation from the reticle and to the microlithographic substrate along a substrate radiation path segment. The reticle is then moved along a reticle path generally normal to the reticle radiation path segment, and the microlithographic substrate is moved along a substrate path. The substrate path has a first component generally parallel to the substrate radiation path segment and a second component generally perpendicular to the substrate radiation path segment. The microlithographic substrate moves generally parallel to and generally perpendicular to the substrate radiation path segment toward and away from the reticle while the reticle moves along the reticle path. In a further aspect of this embodiment, the method can include oscillating the microlithographic substrate toward and away from the reticle along an axis generally parallel to the substrate radiation path segment in a periodic manner. In yet a further aspect of this method, the radiation can include a beam having a beam width at the microlithographic substrate and the microlithographic substrate can be moved for one period during the time the microlithographic substrate moves transverse to the beam by a distance of one beam width or about one beam width.
The invention is also directed toward apparatuses for exposing a radiation-sensitive material of a microlithographic substrate to a selected radiation. In one aspect of the invention, the apparatus can include a source of radiation positioned to direct a selected radiation along a radiation path. The apparatus can further include a reticle positioned in the radiation path with the reticle being configured to pass the radiation toward a microlithographic substrate. The reticle is coupled to at least one actuator to move relative to the radiation path in a direction generally perpendicular to the radiation path. The apparatus can further include a substrate support having a support surface positioned to support a microlithographic substrate in the radiation path with the microlithographic substrate receiving radiation passing from the reticle. The substrate support can be coupled to at least one actuator to move relative to the radiation path along a substrate support path having a first component generally parallel to the radiation path and a second component generally perpendicular to the radiation path. The substrate support can be movable along both the first and second components of the substrate support path while the reticle moves along the reticle path.
In further embodiments, the apparatus can include a substrate support having a support surface positioned to support a microlithographic substrate in the radiation path with a surface of the microlithographic substrate at least approximately normal to the radiation path. The apparatus can further include a reticle positioned in the radiation path and oriented at a first non-normal angle relative to the radiation path. The reticle can be coupled to an actuator to move along a reticle path inclined relative to the substrate path by a second non-normal angle approximately equal to the first non-normal angle. Alternatively, the substrate support can be configured to support the microlithographic substrate at a first non-normal angle relative to the radiation path, and the reticle can be configured to move along a reticle path oriented at a second non-normal angle relative to radiation path.